Self-destroying blasting cap

ABSTRACT

Blasting cap for use in underwater blasting (seismic) exploration having a magnesium or magnesium base alloy casing decomposable in water. A preferred embodiment provides a second metal, having higher electrical potential than the magnesium casing, in strips or bands around the casing. The casing of this invention decomposes in a predetermined immersion time in water whereupon rendering the blasting cap undetonatable.

United States Patent lnventors Josef Prior;

Gottfried Prasnlk. both of Tro'adorl, Germany Appl. No. 776,382 Filed Nov. 18, 1968 Patented Aug. 3,1971 Assignee Dynamlt Nobel Aktiengmellschaft Troisdorl, Germany Priority Dec. 1, 1967 Germany P 16 46 347.1

SELF-DIB'IRQYING BLASTING CAP 5 Claims, 1 Drawing Fig.

US. Cl..... 102/28 M Int. Cl. F42b 3/12 Field of Search 102/24. 28

[56] References Cited UNITED STATES PATENTS 3,358,601 12/1967 Dittmann et al. 102/28 3,372,640 3/1968 Dow et al.. 102/28 3,415,188 12/1968 Ball 102/24 Primary Examiner-Verlin R. Pendegrass Attorney-Burgess, Dinklage & Sprung INVENTORS J OSEF PRIOR GOTTFRIED PRASNIK ATTORNEYS.

PATENTED AUG 31971 SELF-DESTROYING BLASTING CAP This invention relates to blasting caps. it more particularly refers to blasting caps used in underwater blasting.

Underwater blasting, particularly in coastal areas, requires explosives and detonators which will destroy themselves in as short a time as possible after the occurrence of any operator errors or other troubles resulting in a misfire, so that they will not constitute a-hazard if they should be driven ashore. Attempts have been made to solve this problem by providing blasting caps into which sea water can penetrate after a period of time, so that they become wet and their function is substantially impaired. The disadvantage of the use of this known type of blasting cap lies in the fact that it is not detonatable only in the wet state and therefore constitutes no hazard only when wet; it they should float or be driven ashore, they might dry out completely and become entirely operative again.

A blasting cap that can be used without danger for underwater blasting in coastal waters must accordingly meet the following requirements: it must prevent the penetration of water over a certain defined period of time so as to maintain the association existing between the primary charge, the secondary charge and the plug containing the electrical primer. It must also permit the penetration of water after a number of hours for the purpose of destroying the ready-tooperate association between the individual charges. Furthermore, however, after the penetration of water into the individual charges, the assurance must be provided that these charges are permanently separated from one another and not capable of reuniting upon drying out.

A blasting cap which meets these requirements has, according to the invention, an outer shell of magnesium or its binary and/or ternary alloys which are not resistant to water, as for example magnesium alloys with silicon, bismuth, zinc or calcium. However, other base metals or their alloys which can be destroyed by water can be used for the shell.

The rate of decomposition of the blasting cap shell can be regulated according to the invention by bringing the blasting cap shell in close contact with a metal whose normal electrical potential is greater than that of the blasting cap shell. This more noble metal then forms with the metal or alloy of the blasting cap shell, due to the contact between the two metals, a local electric cell. The contact can be brought about, for example, by drawing rings or sleeves of such a metal over the blasting cap shell, or simply by making a certain portion of the shell, which is intended to contain the explosive charge, out of such a metal (cf. example). In the presence of sea water, an electrolytic decomposition of the less noble metal blasting cap shell commences immediately. Depending upon the combination of the metal or alloy of the shell with a more or less noble metal, a more or less strong electrical potential is produced, which leads to a rapid or slower disintegration of the blasting cap shell.

It is furthermore desirable to provide an inner shell inside the blasting cap shell which is also of a metal whose normal electrical potential is greater than that of the blasting cap shell. After the decomposition of the blasting cap shell, the penetration of sea water into the interior of the blasting cap can accelerate the destruction of the blasting cap as a result of the formation of a local electric cell.

EXAMPLE 1 Blasting caps were used as per the drawing hereof which is a sectioned elevation thereof. In this Example, the blasting cap was made up of the following parts: (1) primer, (2) sleeves of nickeled copper, (3) inner shell, also of nickeled copper, (4) primary charge of lead azide, (5) secondary charge of tetryl, (6) magnesium shell. it should be noted that no sleeves 2. were present in this cap. After an immersion time of 1 hour in sea water, it was still possible to fire a blasting cap electrically.

Another blasting cap without sleeves (2) was immersed in together. Such blasting caps could no longer be fired.

EXAMPLE 2.

For these experiments, blasting caps were used according to the annexed drawings, and were equipped with nickel plated copper sleeves 2. They were treated in the same manner as in Example 1. After an hour of immersion in sea water, a blasting cap could still easily be fired. Twelve hours of immersion in sea water, however, resulted in decomposition of the shell and the charges were no longer held together. The blasting cap could no longer be fired.

What I claim is:

1. In a blasting cap adapted for use in underwater applications and comprising a primer, a primary charge, a secondary charge, detonator means and housing means all in operative association with each other; the improvement which comprises said housing means comprising a shell of a first metal which is decomposable in contact with water, a second metal whose normal electrical potential is higher than said first metal in electrical contact with said first metal, which shell surrounds said blasting cap components.

2. The improved blasting cap claimed in claim 1 wherein said housing first metal comprises magnesium.

3. The improved blasting cap claimed in claim 2 wherein said magnesium is in alloy form.

4. The improved blasting cap claimed in claim 1 wherein said housing comprises a shell of said first metal surrounding said blasting cap components and at least one sleeve of said second metal over said shell.

5. The improved blasting cap claimed in claim 1 wherein said housing comprises an outer shell of said first metal and an inner shell of said second metal. 

1. In a blasting cap adapted for use in underwater applications and comprising a primer, a primary charge, a secondary charge, detonator means and housing means all in operative association with each other; the improvement which comprises said housing means comprising a shell of a first metal which is decomposable in contact with water, a second metal whose normal electrical potential is higher than said first metal in electrical contact with said first metal, which shell surrounds said blasting cap components.
 2. The improved blasting cap claimed in claim 1 wherein said housing first metal comprises magnesium.
 3. The improved blasting cap claimed in claim 2 wherein said magnesium is in alloy form.
 4. The improved blasting cap claimed in claim 1 wherein said housing comprises a shell of said first metal surrounding said blasting cap components and at least one sleeve of said second metal over said shell.
 5. The improved blasting cap claimed in claim 1 wherein said housing comprises an outer shell of said first metal and an inner shell of said second metal. 